Calculating work and force on an angle

Example problem: A refrigerator weighing 175lbs is on a 50' ramp. The ramp has an incline of 15*. Find the magnitude of force required to keep the refrigerator from sliding down the ramp and the work required to push the refrigerator up the ramp.

The example says w=FxDcos75 so work =2265ft lbs. I dont really understand how they got this formula.

How do I find out the force to keep the fridge from sliding down the ramp?